Symptoms

1. You are using Microsoft Outlook and set it to keep a local copy of your items on your computer (Offline Outlook Data File *.ost).
2. You create a backup of your machine using VSS.
3. Backup completes successfully.
4. The *.ost-file is not present in the backup.

Cause

This is a limitation of Microsoft (link 1, link 2): due to the current design the *.ost-file is not supposed to be backed up.

Solution

Do the following to work around the issue:

1. Open the Windows Registry Editor (start -> run -> regedit.exe)
2. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\BackupRestore\FilesNotToSnapshot
3. Delete the OutlookOST subkey (marked in green):
   
4. Create a new backup. The backup should contain the *.ost-file.

More information

Please contact Acronis Support if you need assistance.